feat(VocabCourseView): add hard vocabulary practice button and refresh logic

- Introduced a button to start hard vocabulary practice when applicable, enhancing user engagement with challenging vocabulary.
- Implemented methods to manage and refresh the hard vocabulary list from local storage, ensuring users have access to their difficult words.
- Added event listeners to refresh the hard vocabulary list on window focus, improving the overall user experience.

frontend/src/views/social/VocabCourseView.vue

@@ -16,6 +16,14 @@
         <span v-if="course.shareCode && isOwner" class="share-code">
           {{ $t('socialnetwork.vocab.courses.shareCode') }}: <code>{{ course.shareCode }}</code>
         </span>
+        <button
+          v-if="hardVocabCount > 0"
+          type="button"
+          class="course-hard-practice-link"
+          @click="openHardPractice"
+        >
+          {{ $t('socialnetwork.vocab.courses.startHardVocabTrainer', { count: hardVocabCount }) }}
+        </button>
         <button type="button" class="course-dictionary-link" @click="goCourseDictionary">
           {{ $t('socialnetwork.vocab.dictionary.open') }}
         </button>
@@ -345,6 +353,7 @@ export default {
       srsLoading: false,
       showAddLessonDialog: false,
       assistantSettings: null,
+      hardVocabList: [],
       lessonFormTouched: false,
       newLesson: {
         lessonNumber: 1,
@@ -390,6 +399,9 @@ export default {
       }
       return Array.isArray(this.srsDueItems) ? this.srsDueItems.length : 0;
     },
+    hardVocabCount() {
+      return Array.isArray(this.hardVocabList) ? this.hardVocabList.length : 0;
+    },
     dueReviewLessons() {
       return this.sortedLessons
         .filter((lesson) => {
@@ -519,12 +531,45 @@ export default {
   watch: {
     courseId() {
       this.loadCourse();
+      this.refreshHardVocabList();
     }
   },
   methods: {
     displayCourseTitle(course) {
       return localizeVocabCourseTitle(course?.title, this.$i18n?.locale) || '';
     },
+    hardStorageKey() {
+      return this.courseId ? `yourpart:vocab:hardList:${this.courseId}` : null;
+    },
+    refreshHardVocabList() {
+      const key = this.hardStorageKey();
+      if (!key) {
+        this.hardVocabList = [];
+        return;
+      }
+      try {
+        const raw = localStorage.getItem(key);
+        const parsed = raw ? JSON.parse(raw) : {};
+        const values = parsed && typeof parsed === 'object' ? Object.values(parsed) : [];
+        this.hardVocabList = values
+          .map((entry, idx) => {
+            const learning = String(entry?.learning || '').trim();
+            const reference = String(entry?.reference || '').trim();
+            if (!learning || !reference) return null;
+            return {
+              id: `hard-${idx}-${learning}-${reference}`,
+              learning,
+              reference
+            };
+          })
+          .filter(Boolean);
+      } catch (_) {
+        this.hardVocabList = [];
+      }
+    },
+    handleWindowFocus() {
+      this.refreshHardVocabList();
+    },
     async loadCourse() {
       this.loading = true;
       try {
@@ -858,6 +903,14 @@ export default {
         lessonId: lesson.id
       });
     },
+    openHardPractice() {
+      if (!this.hardVocabCount) return;
+      this.$refs.practiceDialog?.open?.({
+        courseId: this.courseId,
+        initialPool: this.hardVocabList,
+        onClose: () => this.refreshHardVocabList()
+      });
+    },
     openSrsPractice() {
       if (!this.srsDueItems.length) {
         return;
@@ -922,6 +975,11 @@ export default {
       this.loadCourse(),
       this.loadAssistantSettings()
     ]);
+    this.refreshHardVocabList();
+    window.addEventListener('focus', this.handleWindowFocus);
+  },
+  beforeUnmount() {
+    window.removeEventListener('focus', this.handleWindowFocus);
   },
 };
 </script>
@@ -978,6 +1036,10 @@ export default {
   margin-left: auto;
 }
 
+.course-hard-practice-link {
+  flex-shrink: 0;
+}
+
 .course-assistant {
   display: flex;
   align-items: flex-start;